+ mm-document-zone-device-struct-page-field-usage.patch added to -mm tree

+ mm-document-zone-device-struct-page-field-usage.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm: document zone device struct page field usage
has been added to the -mm tree.  Its filename is
     mm-document-zone-device-struct-page-field-usage.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/mm-document-zone-device-struct-page-field-usage.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/mm-document-zone-device-struct-page-field-usage.patch

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------------------------------------------------------
From: Ralph Campbell <rcampbell@nvidia.com>
Subject: mm: document zone device struct page field usage

Struct page for ZONE_DEVICE private pages uses the page->mapping and and
page->index fields while the source anonymous pages are migrated to device
private memory.  This is so rmap_walk() can find the page when migrating
the ZONE_DEVICE private page back to system memory.  ZONE_DEVICE pmem
backed fsdax pages also use the page->mapping and page->index fields when
files are mapped into a process address space.

Restructure struct page and add comments to make this more clear.

Link: http://lkml.kernel.org/r/20190719192955.30462-2-rcampbell@nvidia.com
Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mm_types.h |   42 +++++++++++++++++++++++++------------
 1 file changed, 29 insertions(+), 13 deletions(-)

--- a/include/linux/mm_types.h~mm-document-zone-device-struct-page-field-usage
+++ a/include/linux/mm_types.h
@@ -76,13 +76,35 @@ struct page {
 	 * avoid collision and false-positive PageTail().
 	 */
 	union {
-		struct {	/* Page cache and anonymous pages */
-			/**
-			 * @lru: Pageout list, eg. active_list protected by
-			 * pgdat->lru_lock.  Sometimes used as a generic list
-			 * by the page owner.
-			 */
-			struct list_head lru;
+		struct {	/* Page cache, anonymous, ZONE_DEVICE pages */
+			union {
+				/**
+				 * @lru: Pageout list, e.g., active_list
+				 * protected by pgdat->lru_lock. Sometimes
+				 * used as a generic list by the page owner.
+				 */
+				struct list_head lru;
+				/**
+				 * ZONE_DEVICE pages are never on the lru
+				 * list so they reuse the list space.
+				 * ZONE_DEVICE private pages are counted as
+				 * being mapped so the @mapping and @index
+				 * fields are used while the page is migrated
+				 * to device private memory.
+				 * ZONE_DEVICE MEMORY_DEVICE_FS_DAX pages also
+				 * use the @mapping and @index fields when pmem
+				 * backed DAX files are mapped.
+				 */
+				struct {
+					/**
+					 * @pgmap: Points to the hosting
+					 * device page map.
+					 */
+					struct dev_pagemap *pgmap;
+					/** @zone_device_data: opaque data. */
+					void *zone_device_data;
+				};
+			};
 			/* See page-flags.h for PAGE_MAPPING_FLAGS */
 			struct address_space *mapping;
 			pgoff_t index;		/* Our offset within mapping. */
@@ -155,12 +177,6 @@ struct page {
 			spinlock_t ptl;
 #endif
 		};
-		struct {	/* ZONE_DEVICE pages */
-			/** @pgmap: Points to the hosting device page map. */
-			struct dev_pagemap *pgmap;
-			void *zone_device_data;
-			unsigned long _zd_pad_1;	/* uses mapping */
-		};
 
 		/** @rcu_head: You can use this to free a page by RCU. */
 		struct rcu_head rcu_head;
_

Patches currently in -mm which might be from rcampbell@nvidia.com are

mm-document-zone-device-struct-page-field-usage.patch
mm-hmm-fix-zone_device-anon-page-mapping-reuse.patch
mm-hmm-fix-bad-subpage-pointer-in-try_to_unmap_one.patch